1,721,429 research outputs found
Neural correlates of visual imagination
No full textL'immaginazione visiva rappresenta un aspetto fondamentale della nostra vita. Può essere definita come l'abilità di generare immagini visive, simili agli oggetti fisici realmente percepiti, in assenza di uno stimolo retinico.
Vedere un oggetto è sicuramente un'esperienza diversa dall'immaginarlo. Tuttavia, questi due fenomeni mentali appaiono strettamente interconnessi esercitando una reciproca influenza l'uno sull'altro. Ad esempio, esistono studi recenti che mettono in evidenza l'esistenza di circuiti neurali comuni implicati sia nella percezione che nell'immaginazione visive. La definizione dei processi cognitivi coinvolti nell'immaginazione visiva è uno dei settori di ricerca più attivi nell'ambito della psicologia cognitiva come testimoniato dallo "storico" dibattito fra Kosslyn e Pylyshyn sulla natura analogica o preposizionale dell'immaginazione visiva.
La teoria di Pylyshyn sostiene che, come il linguaggio, anche le immagini siano simboliche e abbiano poco in comune con la percezione. Secondo tale approccio teorico non viene ipotizzata un'attivazione delle aree visive primarie durante l'immaginazione. Diversamente, Kosslyn ipotizza che le immagini mentali condividano con la percezione visiva rappresentazioni di tipo analogico...The rationale of the present study was to investigate more closely the neural correlates on which the visual imagery relies on.
Recent fMRI and neuropsychological studies have showed a crucial involvement of the visual areas in the generation of visual mental images. Nevertheless, the neural bases of the visual imagery still controversial and little is known about the cognitive operations that can be carried on the generated mental images. To cast light on this problem, we have studied possible behavioural effects that visual perception and imagery have in common, based either on simple neural physiological features proper of the perceptual system or on complex cognitive operations. In order to do this, we have tested by means of a series of experiments, whether visual effect on reaction time, based on a morpho-functional caratheristic of the visual system, might be replicated also within the visual imagery. A well known effect obtained with visual stimuli concern the increase of the RT with peripheral in contrast of the central stimuli (eccentricity effect)..
Information theory in biochemical regulatory networks: a theoretical study
Full text linkIn this Thesis we consider the optimization of information transmission as a viable design principle for biochemical networks. We apply this principle to a simple model regulatory circuit, given by an input and a delayed output that switch randomly between two states in continuous time.
First we maximize the transmitted information in the network at a given output delay, when the system has no external constraints and it is in steady state or can optimize its initial condition. We find that optimal network topologies correspond to common biological circuits linked to stress response and that circuits functioning out of steady state may exploit absorbing states to be more informative than in steady state.
We then take into account that biological regulatory networks need to dissipate energy in order to transmit biochemical signals and that such signaling often happens in challenging environmental conditions. Hence we explore the system's trade-offs between information transmission and energetic efficiency. At fixed delay and dissipated energy, we determine the most informative networks both in the absence and in the presence of
feedback. We find that negative feedback loops are optimal at high dissipation, whereas positive feedback loops become more informative close to equilibrium conditions. Moreover, feedback allows the system to transmit almost the maximum available information at a given delay, even in the absence of dissipation.
Finally, within a game-theoretic maximin approach, we ask how a biochemical network should be constructed to be most informative in the worst possible initial condition set by the environment. We find that, in the limit of large energy dissipation, the system tunes the ratio of the input and output timescales so that the environmental disturbance is marginalized as much as possible
La visione dell'ebreo in Martin Luther e la sua ricezione nell'età dell'Ortodossia luterana
No full textThe dissertation is about Martin Luther's depiction of the Jew and its influence on Lutheran theologians and preachers in 16th and 17th century-Germany. Most of Lutheran clergymen considered the Jew as a rhetorical device, which could be used to achieve many goals, such as proving the valifity of Lutheran doctrine, imparting catechistic knowledge to the parishioners, and asserting the parson's authority.La tesi di dottorato riguarda la visione dell'ebreo in Martin Luther e la sua ricezione da parte dei teologi e predicatori luterani durante l'età dell'Ortodossia
A PROMISING NOVEL FORMULATION OF STAPHYLOCOCCUS AUREUS VACCINE PROTECTS MICE VIA ANTIBODIES AND CD4+ EFFECTOR T CELLS
Full text linkLife-threatening Staphylococcus aureus infections and the emergence of antibiotic-resistant strains make vaccination a major medical need. Novartis Vaccines developed a vaccine candidate (Combo) that consists of HlaH35L, a non-toxic mutant of the α-toxin, EsxAB, a fusion of the secreted factors EsxA and EsxB, and of two surface proteins, FhuD2 and Sur2. Combo±alum has shown efficacy in pre-clinical mouse models and has recently been tested in a human phase I clinical trial.
To improve this vaccine further, Combo antigens were formulated with alum/SMIP-7.10 (alum-S-7), a novel adjuvant formulation composed of a Toll-like receptor 7 agonist small molecule adsorbed to alum. We characterized the immune responses elicited by this novel formulation, and compared its efficacy to that induced by Combo±alum in a mouse model of S. aureus-induced peritonitis.
Combo+alum-S-7 showed increased efficacy than Combo+alum, with 75%, respectively 40%, of mice surviving a lethal challenge. Compared to Combo+alum, Combo+alum-S-7 induced higher vaccine-specific antibody titers, and polarized CD4+ T-cell responses towards Th1 and Th17 effectors (IFN-ϒ or IL-17 production, respectively). In vivo depletion of CD4+ effector T cells in mice vaccinated with Combo+alum-S-7 reduced the efficacy of this vaccine by 20%. The residual protection was likely due to Combo-specific antibodies since passive transfer of sera from mice immunized with Combo+alum-S-7 to naïve mice resulted in 30% of survival. The requirement of B cells/antibodies to confer protection against S. aureus in the peritonitis model by Combo vaccination was confirmed by the death of 96% of B-cell ko JH mice vaccinated with Combo+alum/S-7 or Combo+alum. In vivo neutralization of IL-17A, either alone or together with IFN-ϒ, but not of IFN-ϒ alone, increased bacterial loads in kidneys of mice immunized with Combo+alum-S-7 as did the depletion of CD4+ effector T cells.
Overall these data show that adding SMIP-7.10 to Combo+alum increases the efficacy of this candidate vaccine through combined antibody and Th17 responses in an animal model of S. aureus infection
Can IPS reach Visual awareness without V1? evidence from TMS in healthy subjects and hemianopic patients.
No full textTMS of the occipital cortex can elicit conscious visual percepts, the so-called phosphenes, i.e. the experience of flashes of light in the absence of an external stimulus. Previous evidence has shown that phosphenes can be elicited by TMS of the intraparietal sulcus (IPS). Here, we tested whether IPS-phosphenes are generated without any contribution from the occipital cortex. In Experiment 1, healthy subjects showed that parietal phosphenes were reliable different in terms of threshold, highly variable in size and, in contrast to the occipital ones, they did not change in lateralization within the visual field. Moreover, to strengthen these results and to ascertain whether feedback to primary visual cortex is necessary for visual awareness to emerge, in Experiment 2, we induced phosphenes by applying TMS over the parietal cortex of the lesioned hemisphere in two hemianopic patients with a complete destruction of primary visual cortex. For both patients we found that they could perceive phosphenes, that a psychophysical threshold function could be created and that this function was not different from that obtained with healthy subjects. In addition, they could reliably draw the phosphenes and position them within their blind field and they could reliably score the phenomenical characteristics of their phosphenes both in terms of vividness and brightness in a manner similar to healthy subjects. The two brain-damaged patients have thus shown that stimulation of visual areas within the intraparietal sulcus of their lesioned hemisphere, can, in fact, elicit conscious visual percepts. These results seem to demonstrate that TMS-induced visual phenomenology over IPS can generate conscious visual percepts and, more importantly, that it does so independently of any contributions from the primary visual cortex
Interhemispheric transfer of phosphenes induced by occipital versus parietal cortex TMS.
No full textInterhemispheric transfer and integration of imagined visual stimuli
No full textWe employed two reaction time paradigms to find out whether imagined visual stimuli can be integrated between the two cerebral hemispheres. In a first experiment we found that interhemispheric transfer time, as assessed with the Poffenberger paradigm, was much longer for imagined than visible stimuli and this suggests that the callosal site of transfer is different in the two conditions. In a second experiment we found that interhemispheric summation, as assessed with the redundant signal effect paradigm, was present for both visible and imagined stimuli and could be accounted for by a neural coactivation mechanism rather than by a probabilistic explanation. Taken together, these results support the view that that there is an equivalence between perceptual and imagery processes that goes beyond early processing stages and includes the interhemispheric exchange of information
Interhemispheric transfer of phosphenes generated by occipital versus parietal transcranial magnetic stimulation
No full textPhosphenes represent a perceptual effect of transcranial magnetic stimulation (TMS) or electric stimulation of visual cortical areas. One likely neural basis for the generation of static phosphenes is the primary visual cortex (V1) although evidence is controversial. A peculiar feature of V1 is that it has sparse callosal connections with the exception of a central portion of visual field representation. In contrast, visually responsive cortical areas in the parietal lobe have widespread callosal connections. Thus, interhemispheric transfer (IT) time of off-centre phosphenes should be slower when generated by V1 than by visual parietal areas. To verify this possibility, in Exp. 1 we measured IT of phosphenes generated by TMS applied to V1 and in Exp. 2 we measured IT of phosphenes obtained by TMS applied to posterior parietal cortex. In both experiments, we obtained static bright circular phosphenes appearing in the contralateral hemifield. We measured IT time behaviorally by comparing unimanual simple reaction time to the onset of a phosphene under crossed or uncrossed hemifield-hand condition (Poffenberger paradigm). In keeping with our prediction, we found a substantially longer IT time for V1 than for parietal phosphenes. Additionally, an IT similar to that obtained with V1 stimulation was found when participants were asked to imagine the phosphenes previously experienced during TMS. In conclusion, the present results suggest that IT of phosphenes either generated by V1 TMS or imagined is subserved by slower callosal channels than those of real visual stimuli or parietal phosphenes
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